1. Field of the Invention
The present invention relates to a method of manufacturing a group-III nitride crystal, and in particular to a method of manufacturing a group-III nitride crystal with the growth rate thereof increased.
2. Description of the Background Art
As is well known in the art in recent years, there has been an increased demand for a gallium nitride (GaN) crystal or any other similar group-III nitride crystal to use, for example, in a semiconductor laser and a semiconductor light emitting diode for emitting blue light or ultraviolet light.
As a conventional method of manufacturing a group-III nitride crystal, there is known a hydride vapor deposition method, an organic metal vapor deposition method, a chemical transport method, or the like.
In the hydride vapor deposition method and the organic metal vapor deposition method, however, a source gas is introduced into a reaction chamber for a reaction, in which hydrogen chloride (HCl), ammonia (NH3), hydrogen (H2) or the like is not incorporated into a group-III nitride crystal as its component, remains in the reaction chamber, and is required to be evacuated therefrom. Therefore, in these methods, most of the source gas is disposed without contributing to the growth of a group-III nitride crystal, which causes lower material yields. Furthermore, disposing a large amount of gas such as HCl, NH3 or H2 requires large facilities to eliminate toxicity thereof, which also causes higher cost of production facilities.
In contrast, in the chemical transport method in which a source gas vaporized in a high-temperature portion of a closed reaction pipe is transported to a low-temperature portion thereof to grow a crystal there, the gas is not evacuated from the pipe, providing favorable material yields. In this method, however, a source gas is not supplied from outside. Therefore, an amount of the source gas to be transported cannot be increased, making it difficult to increase the growth rate of a group-III nitride crystal.
Furthermore, U.S. Pat. No. 5,868,837, Japanese Patent Laying-Open Nos. 2001-58900, 2001-64097, 2001-64098, 2001-102316, and 2002-201100 disclose a method of growing a GaN crystal by means of a flux method in which sodium (Na) or the like is used as a flux. However, in the method disclosed in the patent literature above, a high-pressure container is required to cope with the low growth rate of a GaN crystal, which also causes higher cost of manufacturing the same. In addition, the method suffers from difficulty in controlling electrical conduction of the GaN crystal.